This application relates to and claims priority to corresponding Japanese Patent Application No. 320483/1999, which was filed on Nov. 11, 1999, and which is incorporated by reference herein.
(1) Field of the Invention
The present invention relates to an optical digitizer, which detects the position coordinates where a finger, a stylus or a pointing stick (hereinafter refer to as a pointing instrument) points on a coordinate plane, and more specifically, to an optical digitizer, which recognizes kinds of pointing instruments and enables an input by a finger or a pen.
(2) Description of the Related Art
In recent years, mobile type pen input computers, such as PDA, are becoming increasingly popular. Many of them have pressure-sensitive resistance membrane system touch panels placed on front of LCD display devices, enabling a user to operate the computer and input a drawing by touching the touch panel, or by drawing with a finger or a pen, so that the user can use it in the same way as a normal pen and a notebook. However, in the case of inputting a signature for signature verification, or inputting a medical record into a patient""s file, in which a handwriting input is important, if the user touches the touch panel with a hand, it becomes an error input due to the characteristics of the touch panel. This is called the hand-touch problem. Moreover, in the pressure-sensitive resistance membrane system touch panel, there are occasions where the surface membrane is torn by a pen due to its structural characteristics. In order to avoid such problems, an optical system digitizer has been proposed in lieu of the pressure-sensitive resistance membrane system touch panel.
FIG. 1 illustrates an example of the conventional optical digitizers. A tunnel mirror 14 is disposed in front of an image forming lens 9 for a linear image sensor 13, and a pair of detecting units, wherein each of the units is arranged in such a manner that a light axis of an LED light source 31 coincides with a light axis of the linear image sensor 13, are arranged in the peripheral area of a coordinate plane 1. The tip of a pointing instrument 2, such as a pen, is wrapped with a tape 22 composed of a retroreflective material. When a light ray emitted from LED light source 31 is irradiated on the retroreflective tape 22 at the tip of the pen 2, the incident light returns straight back to where it came from due to the retroreflective characteristic. The image of this reflected light is taken by the right and left side linear image sensors 13, and converted to an electric signal. The signal is then processed at the coordinate computing section 7 by using the triangulation principle to detect the pointed coordinates of the pen tip. In this case, unless a hand intercepts between the pen tip and the image taking means, a hand-touch is allowed. However, in this conventional example, an input by a finger cannot be made. Therefore, it cannot be used as a touch pad loaded on a notebook-type personal computer or as a simple touch panel.
Another example of a conventional optical digitizer is illustrated in FIG. 2. In the conventional example illustrated in FIG. 1, the retroreflective material is installed at the tip of the pen 2, but in the conventional example illustrated in FIG. 2, the retroreflective material is installed on the frame of the coordinate plane 1. In this case, the images in the retroreflective material 4 positioned at the two sides of the coordinate plane 1 are taken by each of the right and left image sensors 13. In other words, the right-side image sensor takes the images 4a and 4b of the retroreflective material, and the left-side image sensor takes the images 4b and 4c, respectively. When a pointing instrument 20, such as a finger, is placed on the coordinate plane 1, the reflected light from the retroreflective material 4 is intercepted by the pointing instrument 20, and the shadow image 20a is detected by the image sensor 13, which makes it possible to detect the pointed coordinates of the pointing instrument 20.
A conventional optical digitizer as illustrated in FIG. 1 allowed to input by a special pen only, which requires a pen even for making a simple input through a touch panel. Moreover, since it requires a specific pen, when it is loaded on a notebook-size personal computer, it is often inconvenient for a user. The conventional digitizer as illustrated in FIG. 2 served the purpose as far as the inputting by a pen is concerned, but it did not solve the hand-touch problem.
To solve these problems, the present invention aims to provide an optical digitizer, which has the function to recognize kinds of pointing instruments, and enables an input by both a finger and a pen. Moreover, the invention aims to provide an optical digitizer with a pointing instrument equipped with a plurality of functions by installing a supplemental information transmission means into the pointing instrument.
In order to accomplish the above mentioned objectives, the present invention relates to an optical digitizer which detects a position coordinate pointed by a pointing instrument on a coordinate plane, and has a function to recognize a first pointing instrument, which is not equipped with a retroreflective material, from a second pointing instrument, which is equipped with the retroreflective material at its tip, wherein the optical digitizer is comprised of a light source for emitting a light ray, an image taking means, which is placed in the periphery of the coordinate plane to take an image of the pointing instrument by using the light ray of the light source and convert the taken image into an electrical signal, a computing means for computing the position coordinates by processing the electrical signal converted by the image taking means, a light polarization means which is provided at the light source for polarizing the emitted light from the light source into a first polarized light or a second polarized light, a switching means with which irradiating light to the coordinate plane is switched to the first polarized light or the second polarized light, a retroreflective material having retroreflective characteristics which is provided on a frame of the coordinate plane, a polarizing film installed in front of the retroreflective material and having a transmitting axis to cause the first polarized light to be transmitted, and a judging means for judging the pointing instrument as a first pointing instrument if the image of the instrument is taken by the first polarized light, and for judging the pointing instrument as a second pointing instrument if the image of the instrument is taken by the second polarized light.
The light source means is comprised of two sources, and the polarizing means is comprised of the first polarizing means, which allows the first polarized light to transmit, and the second polarizing means, which allows the second polarized light to transmit, both the polarizing means being installed at each light source, and the first polarized light and the second polarized light are alternately illuminated by irradiating the two light sources alternately through the switching means.
It may also be arranged that the polarizing means comprises a first polarizing means, which allows the first polarized light to transmit, and a liquid crystal plate, so that the first polarized light and the second polarized light are illuminated by switching voltages applied to the liquid crystal plate by a switching means.
Further, the present invention relates to an optical digitizer which has a function to recognize kinds of a pointing instrument, wherein the optical digitizer is comprised of a light source to emit a light ray, an image taking means, installed in the peripheral area of the coordinate plane to take an image of the pointing instrument by using the light ray of the light source and to convert the taken image into an electrical signal, a calculation means to compute the pointed position coordinates by processing the converted electrical signal through the image taking means, a polarizing means which is installed in the image taking means to make the incident light as the first polarized light or the second polarized light, a dividing means to divide the incident light to the image taking means, a retroreflective material installed at the frame of aforementioned coordinate plane, which has retroreflective characteristics, a polarizing film which is installed in front of the retroreflective material, having a transmitting axis to cause the first polarized light ray to be transmitted, and a judgment means which judges the pointing instrument as a first pointing instrument if the image of the instrument is taken by the first polarized light, as a second pointing instrument if the image of the instrument is taken by the second polarized light, and as the second pointing instrument if the image of the instrument is taken by both the first and the second polarized light.
The present invention further relates to an optical digitizer wherein the light source means is comprised of two light sources, further having a third polarizing means to cause the first polarized light to be transmitted, and a fourth polarized means to cause the second polarized light to be transmitted, both of them are installed at each of the two light sources, the optical digitizer further having a switching means to cause the two light sources alternately to be emitted, the second pointing instrument having a liquid crystal material at its tip, the optical digitizer further having a judging means to judge the state of the second pointing instrument in the case where the image of the pointing instrument is taken by the second polarized light, by the polarized light which comes into the image taking means in which the polarized light changes by the voltage applied to the liquid crystal material.
The first polarized light ray may be a vertically polarized light ray, and the second polarized light ray may be a horizontally polarized light ray.